Tobacco undergoes several treatment steps before it is ready to be formed into cigarettes and the like. The shredded tobacco is fed to a tobacco enhancement apparatus which is used to increase the effective volume of the tobacco by causing it to expand or "puff".
In one method, the tobacco is passed over an elongate tray formed with a heated plenum having a closely spaced matrix of nozzle openings. The plenum is heated to a temperature of approximately 145.degree. C. by steam passing through the openings, thereby causing the tobacco shreds to expand. In the case of pressurized steam existing within the plenum at pressures of up to 1 MPa, the plenum can be heated to a temperature of up to 180.degree. C. The individual tobacco shreds tend to form a mat which comes into direct contact with the heated plenum and the high temperature steam in the region of the openings; this tends to adversely affect the quality of the tobacco. In addition, due to the large volume of steam passing through the nozzles in the matrix, and the free volume above the mat, the above described process is not extremely energy efficient.